Frequency regulator for tuning fork drive system



April 1, 1969 P. G. KUEFFER 3,435,609

FREQUENCY REGULATOR FOR TUNING FORK DRIVE SYSTEM `Original Filed Oct.18, 1965 1N vENToR PHILIPPE G. //'EFFER United States Patent G 3,435,609FREQUENCY REGULATOR FOR TUNING FORK DRIVE SYSTEM Philippe G. Kuelfer, LaSalle, Ill., assignor to General Time Corporation, New York, N.Y., acorporation of Delaware Original application Oct. 18, 1965, Ser. No.497,236. Divided and this application May 10, 1967, Ser.

Int. Cl. G04c 3/00 U-S. Cl. 58-23 2 Claims ABSTRACT OF THE DISCLOSUREThis application is a divisional of my copending application Ser. No.497,236, iiled Oct. 18, 1965.

This invention relates generally to timepiece driving systems and, moreparticularly, to an improved speed regulator for an electromagneticdrive system in which a tuning fork is used as the frequency or speedcontrolling element.

It is a primary object of the present invention to provide an improvedtimepiece driving system using a tuning fork as the speed controllingelement and in which the vibratory frequency of the tuning fork can beaccurately adjusted in order to adjust the speed of the timepiece. Arelated object f the invention is to provide such an improved tuningfork drive system in which the frequency regulator can be preciselyadjusted by simple and convenient manual operation.

It is another object of one aspect of this invention to provide animproved frequency or speed regulator of the foregoing type which doesnot disturb the balance of the tuning fork being regulated. In thisconnection, it is yet another object of this invention to provide suchan improved regulator device which does not increase the physical sizeof the drive system which vibrates the tuning fork.

It is a further object of the present invention to provide an improvedfrequency regulator of the type described above which regulates thedriving forces applied to the tuning fork rather than superimposing anauxiliary load on the fork tines. Thus, it is a related object toprovide such a regulator which does not interfere with the normalvibratory motion of the tuning fork tines.

Other objects and advantages of the invention will become apparent uponreading the following detailed description and accompanying drawings, inwhich:

FIGURE 1 is a schematic illustration of a tuning fork adapted to drive arotary timepiece, and associated electromagnetic drive means forvibrating the tuning fork at a predetermined frequency.

FIG. 2 is a fragmentary section showing one embodiment of the improvedregulator provided by this invention for controlling the frequency ofthe tuning fork in a system such as illustrated in FIG. l;

FIG. 3 is an end view of one of the cooperating faces of the two coresections in the regulator device of FIG. 2;

FIG. 4 is a fragmentary section showing the core structure for anotherembodiment of the frequency regu- ICC lator provided by this inventionin a tuning fork drive system of the type illustrated in FIG. l;

FIG. 5 is a fragmentary section of still another embodiment of thefrequency regulator provided by this invention; and

FIG. 6 is a fragmentary section showing a fourth embodiment of theimproved regulator of this invention.

While the invention will be described in connection with certainillustrated embodiments, it will be understood that it is not intendedto limit the invention to these embodiments but, on the contrary, it isintended to cover all alternative embodiments, constructions andequivalent arrangements.

Turning now to the drawings, and referring to FIG. l, there is shown atimekeeping standard in the form of a tuning fork 10 made of a magneticilux conducting material and adapted to drive the indicating hands of arotary timepiece via the pinions and gears which comprise theconventional timing train. In order to couple the tines of the tuningfork 10 to the timing train, two C-shaped magnets 11, 12 are mounted onthe ends of the respective fork tines 13, 14 for cooperating with atoothed rotor (not shown) as described in more detail in copendingapplication Ser. No. 492,793 entitled Improved Drive System for TuningFork Timepiece, led Oct. 4, 1965, which is assigned to the assignee ofthe present invention. It will suflice to say that the rotor is drivenat a timed rate which depends upon the frequency of vibration of thefork. While the illustrative tuning fork includes a pair of magnets 11,12 coperating with the rotor, it will be understood that only one magnet(mounted on one of the tines) may be used with a balancing Imass mountedon the other fork tine.

For the purpose of driving the tuning fork, a coil assembly 20 isprovided including a pickup coil 21 and d rive coil 22 wound about amagnetic core 23. As shown in FIG. 1, the pickup coil 21 is connected inthe base or input circuit of a transistor T while the drive coil 22 isconnected to the transistor output circuit which includes a battery Bconnected to the emitter. A capacitor-resistor series circuit RC isconnected in parallel with the pickup coil as shown. Alternate halfcycles of the voltage fluctuations induced in the pickup coil areamplied by the transistor to produce driving pulses in the drive coil 22in proper phase relationship to sustain the tuning fork vibrations. Thedriving pulses produced in the drive coil 22 vary the magnetic ilux inthe air gaps 24, 25 between the two outer ends of the core 23 and therespective fork lines 13, 14, these air gaps 24, 25 forming part of anoverall magnetic circuit which includes both the magnetic core 23 andthe ilux conducting tines 13, 14 of the tuning fork. For the moredetailed features of the electronic circuitry and a more completediscussion thereof, reference is Imade to the above-mentioned copendingapplication.

In accordance with the present invention, the electromagnetic drivesystem for vibrating the tuning fork is provided with an improvedfrequency regulator which comprises means for adjusting the magneticflux in the air gaps 'between the ends of the magnetic core member andthe respective opposed tines of the tuning fork so as to control thevibratory frequency of the tuning fork. Thus, referring to FIG. 2, themagnetic core consists of two cooperating magnetic core sections 30, 31having a pair of opposed abutting end faces 32, 33 which are adapted tovary the magnetic reluctance of the core assembly upon relative rotationof the two sections 30, 31. More particularly, the two cooperating endfaces 32, 33 are generally D-shaped ('FIG. 3) with each D extendingbeyond or encompassing the common axis of the two core sections andforming complemental D-shaped recesses or cavities 34, 35. As one of thecore sections is rotated relative to the other section, the twocooperating D faces 32, 33 overlap more or less with each other so as tovary the contact area 36 between the two sections, thereby varying theflux-carrying capacity of the core assembly and of the magnetic circuitin which the core assembly is included.

In order to facilitate rotation of one of the core sections relative tothe other, a serrated adjustment wheel 37 is secured to the outer end ofthe left-hand core section 30. As the adjustment wheel 37 is turnedthrough any given angular displacement, the left-hand core section 30 isrotated through the same angular distance so as to increase or decreasethe contact area 36 between the two cooperating D faces 32, 33. If thecontact area 36 is increased, the magnetic reluctance of the coreassembly is decreased with an attendant increase in its flux-carryingcapacity. This increases the frequency of the vibratory motion of thetuning fork by increasing the magnetic flux in the air gaps between thetwo outside end faces of the magnetic core and the respctive fork tines.Since the two D faces of the core sections 32, 33 extend beyond orencompass the common axis of the two core sections, it will beappreciated that the two cooperating faces will always be in contactwith each other, with the contact area 36 being reduced or enlarged bysimply rotating one of the two sections relative to the other.

Since the regulator of FIGS. 2 and 3 simply utilizes a drive coreassembly made of two sections instead of one,

it does not increase the physical size of the electromagnetic drivemeans. Moreover, the adjustment Wheel 37 for rotating one of the coresections relative to the other can be made extremely thin and mountedalong one -face of the core assem'bly so that again the physical size ofthe unit is not substantially enlarged. These considerations areextremely important when one considers the limited space available formounting a drive unit of this type between the tines of a miniaturetuning fork. Of course, it will be understood that the cooperating coresections may be provided with configurations other than the D-shaped endfaces used in the illustrative embodiment, as long as the `contact areais varied as one core section is rotated relative to the other.Moreover, the cooperating ends of the core sections may be designed soas to move the two core sections axially relative to the fork tines asone or the other of the sections is rotated. In this latter case, thetwo core sections are preferably moved together through the same axialdistance so as to maintain substantially equal air gaps between theoutside ends of the core and the cooperating fork tines.

An alternative embodiment of the inventive regulator, illustrated inFIG. 4, varies the magnetic flux in the two air gaps without alteringthe magnetic reluctance of the core member. Thus, the regulator deviceof FIG. 4 includes a single core member `40 having a pair of outside endfaces 41, 42 `which cooperate with the fork tines 13, 14 to form a pairof substantially equal air gaps 43, 44. In order to vary the magneticflux within the air gaps, a C- shaped shunt member 45 made of a magneticux conducting material is operatively associated with the core member40. For the purposes of permitting adjustment of the magnetic shunt 45,it is provided with a vertical mounting post 46, the upper `end of whichis threaded into a corresponding threaded socket 47 so that the shunt 45can be raised and lowered relative to the core member 40. As .the shunt45 is raised, the air gaps between the two end faces 48, 49 and the Core40 are increased so that more flux is permitted to llow through the coremember. This increases the frequency of ,the tuning fork by increasingthe ux in the two air gaps 43, i44 between the core end faces 41, 42 andthe cooperating fork tines. Conversely, if the shunt 45 is loweredcloser to the magnetic core 40, more magnetic 'ux is passed through theshunt so as to reduce the flux in the core member and thus in the twoair gaps 43, 44, thereby reducing the frequency of the Vibrating fork.

In accordance with another aspect of this invention, a frequencyregulator is provided for adjusting the magnetic iiux iu the core-tineair gaps by the use of a single core member. Thus, referring to FIG. 5,a single magnetic core 50 is mounted for movement back and forth alongits axis between the tuning fork tines 13, 14. In the particularstructure illustrated, one end of the core 50 is provided with athreaded sleeve 51 which cooperates with a complementally threadedsleeve 52 fitted within the central opening of the pickup coil 21. Inorder to move the core 50 axially in either direction, a serratedadjustment wheel 53 is connected to the threaded sleeve 52. Then as theadjustment wheel 53 is turned through a given angular displacement, thethreaded sleeve 52 is turned through the same distance so as to move themagnetic core 50 along its axis toward one of the tuning fork tines 13,14. Of course, the particular direction in which the magnetic `core v50is moved depends on the direction in which the adjustment wheel 53 isturned.

It can be seen that the regulator of FIG. 5 does not modify the magneticreluctance of the core member 50, nor does it shunt -any of the magneticux between the two ends of the core member. Of course, as one end of thecore member 50 is moved a given distance toward one of the fork tines,the opposite end of the core will be moved away from the other fork tineby the same distance so that the air gaps between the ends of the coremember and the for-k tines are not always equal. Consequently, thisparticular embodiment of the inventive regulator is not most useful inthose applications where it is not essential to maintain perfect balancebetween the two tines of the tuning fork.

In FIG. 6, there is illustrated another type of regulator device whichdoes not form part of the present invention, but which may be helpfulfor comparative purposes. In this device, the frequency of the tuningfork is not regulated by varying the magnetic ilux in the air gapsbetween the two ends of the core member and the respective tuning forktines, but rather by superimposing an auxiliary load on one of thetuning fork tines. Thus, a permanently magnetized screw 60 is threadedinto a brass mounting bracket 61 alongside one of the tuning fork tines.By advancing or retracting this magnetized screw '60 within the mountingbracket 61, a variable supplemental magnetic load is applied to thevibrating fork. In other words, the magnetized screw provides a dampingeffect on the vibrating fork, and the degree of damping applied may bevaried by mechanical adjustment of the screw.

It can be seen from the foregoing detailed description that thisinvention provides an improved timepiece driving system using a tuningfork as the speed controlling element and in which the vibratoryfrequency of the tuning fork can be accurately adjusted in order toadjust the angular velocity of the timepiece. Precise adjustments can bemade by simple and convenient manual operations, such as -by turning theserrated adjustment wheel in the embodiments of FIGS. 2 and 5, or byturning the stem of the magnetic shunt in the embodiment of FIG. 4.Moreover, the preferred regulator devices provided by this inventionmaintain the symmetry of the magnetic circuit and thus do not disturbthe balance of the tuning fork being regulated. Furthermore, theinventive regulator is relatively simple to manufacture at a low cost,and functions by regulating the driving forces applied to the tuningfork rather than superimposing an auxiliary load on the fork tines. Thisregulator is also extremely compact and does not substantially increasethe physical size of the drive system, and does not interfere with thenormal vibratory motion of the fork tines.

I claim as my invention:

1. In a timepiece driving system, the combination of a tuning forkhaving a pair of opposed tines made of a magnetic flux conductingmaterial for controlling the angular velocity of the driving system,electromagnetic drive means including a pair of coils and a magneticcore for vibrating the tuning fork tines, said magnetic core beingpositioned between the tines of the tuning fork to dene predeterminedair gaps between the ends of said core and the tuning fork tines, andadjusting means for moving said magnetic core back and forth along itsaxis relative to the tuning fork tines so as to vary the magnetic fluxin said air gaps and thereby control the vibra tory frequency of thetuning fork, including a threaded sleeve tted over one end of said coreand a cooperating complementally threaded sleeve iitted with at leastone of said coils, and an adjustment wheel for turning one of saidsleeves to move said core relative to said tines, said adjustment wheelextending beyond at least one of the longitudinal edges of the adjacenttine to facilitate turning thereof even while the tuning fork isvibrating.

2. In a timepiece driving System, the combination of a tuning forkhaving a pair of opposed tines made of a magnetic ux conducting materialfor controlling the angular velocity of the driving system,electromagnetic drive means including a pair of coils and a magneticcore for vibrating the tuning fork tines, said magnetic core beingpositioned between the tines of the tuning fork to deiine predeterminedair gaps between the ends of said core and the tuning fork tines, a pairof cooperating threaded sleeves mounted on one end of said magnetic coreand on the coil assembly between the tines of the tuning fork for movingthe magnetic core back and forth along its axis relative to the tuningfork tines So as to adjust the magnetic flux in said air gaps andthereby control the vibratory frequency of the tuning fork and anadjustment wheel for turning one of said sleeves to move said coreyrelative to said tines, said adjustment wheel extending beyond at leastone of the longitudinal edges of the adjacent tine to facilitate turningthereof even while the tuning fork is vibrating.

References Cited UNITED STATES PATENTS 3/1960 Godbey 58-23 5/ 1963Cunningham 84-409 U.S. Cl. X.R. 84--457; 331--156

